It was time to take a better look at tunnel nineteen.

Johansen wasn't around so I collared Hunter. As an afterthought I belted on my patrol pack as well and we went down to the Port Authority at the up-axis hub. Jocelyn Merral was Port Chief, a handsome woman in her fifties-iron-gray hair and a penetrating gaze. We asked her to shut down the tunnel so we could go over it with a fine-tooth comb. She didn't get upset, she just refused. It would be too disruptive to her operations. Tunnel nineteen had been shut down for maintenance and investigation already. The backlog had kept a s.h.i.+p overtime at the down-axis hub. Did I have any idea how much that cost? It wasn't going to happen again.

I couldn't just order it done. The Port Authority is its own police within its jurisdiction. I tried to reason with her. "Ma'am, we are investigating a murder that involves the Isolationists and the smuggling of UN weapons to Wunderland. Surely the Port Authority is as interested in resolving this as we are."

She spoke slowly and firmly. "The Port Authority is not at all interested in shutting down transport tunnels at the casual whim of the ARM."

"Casual whim" was the key phrase. What she meant was that if we wanted her cooperation we were going to have to supply more information. I didn't want to do that. The odds were long someone in the Port Authority was involved with the smugglers, and as one of a handful with command access to the trans.h.i.+p net Merral was high on the suspect list.

Instead, I tried bargaining. "Look, we just need to inspect tunnel nineteen. Can that be done without shutting it down?"

"Certainly, I have just the thing." I was startled by her ready agreement. Information is currency to me, dealing for it is second nature. Merral had just been concerned about the efficiency of her operation. I wasn't used to taking people at face value.

She ushered us out of her office. The gravity was about a twentieth of a G and the corridors had static fields in the floor to aid traction. Merral walked in effortless forty-foot strides. Hunter moved with easy feline grace. I kept unsticking myself and hitting my head on the ceiling before settling awkwardly back to the ground. They had the manners not to laugh too much.

We left the corridor and entered the hub itself, a vast s.p.a.ce full of container racks. I'd been in tunnel nineteen myself but there were no containers in it then. The files on the s.h.i.+pping system contained diagrams of the containers and the hubs but they gave no concept of the scale.

s.h.i.+pping containers are ten meters square and twenty long. The down-axis hub is a hollow cylinder, a klick across and half that deep. Eight rows of storage racks line the hub-twenty-four thousand containers in hundred-meter piles. From any given point inside the cylinder the floor slopes upwards at an impossible angle and the looming racks seem about to topple over. Eventually the floor becomes what common sense dictates is a wall with the rows of racks marching up it with no respect for the gentle but insistent one-twentieth G tug beneath your feet. Farther still the wall becomes a ceiling with the racks dangling from it like ma.s.sive swords of Damocles. Containers are moved simply by launching them from the rack sorters on gentle trajectories either to the docking hub at the center of the cylinder or one of the tunnel entrances around its edge. The empty s.p.a.ce in the middle of the cylinder was full of containers in free fall and I had to consciously keep myself from cringing as they flew overhead with quiet rushes of air.

I felt like a mouse in a warehouse, scampering to avoid being crushed by the frenetic, incomprehensible activity going on overhead.

Merral was watching me. "Impressive, ay?" she asked.

"Impressive isn't the word. I can't believe you let those things go in free fall."

She laughed. "It looks like disaster in motion, doesn't it? Actually it's very safe. There are eight hundred sixty-one trajectories. Whenever one is in use, all the intersecting flight paths are locked out until the container is down and clear of its destination."

I looked up at the graceful, ponderous, hundred-thousand-tonne aerial ballet. It wasn't that I doubted her, but it was hard to shake the feeling all those containers were going to fall on me as soon as G.o.d cut the strings.

Our destination was a cargo box, but this one had doors and large windows cut in the sides. Powerful lights were mounted flush with the walls. Jocelyn thumbed a door open and waved us in. "We use this for troubleshooting and inspections. It carries everything we need, and we don't have to shut down a tunnel to use it."

Inside the container was mostly empty s.p.a.ce. There were doors and windows in the floor and ceiling as well as the walls and all the surfaces were padded and well equipped with handholds. Strapdown chairs with mounts that locked into the handholds were set up beside the forward windows. A quarter of the bottom rear was given over to a series of cabinets that housed batteries, switches and various tool chests.

Beneath the forward window there was a spartan control board with a compact data terminal as well as various b.u.t.tons, gauges and comm gear. Beside it was a small keypad. I recognized it at once from the trans.h.i.+p operations manual. It was the container's s.h.i.+pping control panel, a duplicate of the one mounted on the outside.

I walked over and examined the panel. When Jocelyn joined me, I asked, "This contains the trans.h.i.+p codes?"

"Not just the codes, everything about the s.h.i.+pment. The freight manifest, maximum and minimum allowable temperatures, power requirements, loading parameters, whether the container is pressure sealed, center of ma.s.s, priority level, customs codes, COD status and charges. Everything." She tapped a few keys and cryptic data slid over the small screen inset on the panel. PRI, COD, KPA, BOT, and others along with numbers that didn't mean anything to me. I did recognize two codes. SRC and DST indicated the container's source and destination-both were rack addresses in the up-axis hub.

I tapped a few keys and managed to bring up the DST code. "Can you set this up to go anywhere?" I asked Merral.

"Anywhere on Tiamat. The lockouts don't allow us to be loaded for an offworld destination. This container isn't vacc sealed. I'll set it for the outbound receiving racks at the down-axis hub with a routing override so we get tunnel nineteen. That'll take us right through Tiamat."

It was better than I'd hoped for. "Can you try TMU19J234C?" I asked.

She looked at me with the half accusing "How do you know what that means?" look that's usually reserved for medical patients who show their doctor some basic piece of medical knowledge. Specialists hate it when you trespa.s.s on their specialty. It makes them less special. Nevertheless, she thumbed the pad to authorize the change and punched in the destination code. After a couple of seconds the screen displayed accepted, then reverted to DST: TMU19J234C.

"This transaction is now logged in the transport net, correct?" I asked.

Merral nodded, adjusting the restraining straps that held her in her seat. She motioned for me to do the same.

"Is there any way to circ.u.mvent that?" I asked, fumbling with the belts.

"How do you mean?"

"Can you enter destinations into this panel without having the system become aware of it."

"It could be done. You'd have to block the scan transceiver and trick the panel into thinking it had transmitted the change and received a valid authorization verification. It wouldn't be easy, we use dynamic encryption. Why would you want to?" She reached over and helped me get buckled in.

"A smuggler might change an onworld destination for an offworld destination, or perhaps just make a s.h.i.+pment the system isn't aware of."

"I see what you're getting at, but you misunderstand me. If you prevent the panel from talking to the net, the net will just ignore it. It won't get sent anywhere. There's a lot of ways to break the system, but once it's broken it won't work properly."

"I don't follow."

"Look, the system is vulnerable to tampering and there's no way to avoid that. Rather than try to make it tamper-proof we've made it fail-safe. Getting a container to move involves a series of steps, with our control procedures built into the chain. If any link is broken the system flashes us a trouble warning and won't move the container."

"And the data in the panel itself is all self-encrypted so you need a Port Authority ident to change it, correct?"

Merral warmed to her topic. She obviously enjoyed having someone show an interest in her work. It probably didn't happen too often. "Not quite. The source address is always locked so we can back-trace a s.h.i.+pment, n.o.body can change that. When the s.h.i.+pment arrives and is accepted, the destination address is copied to the source so the container can be sent out again. Manifest, COD charges and destination are set by the s.h.i.+pper and then locked when the PA verifies and seals the s.h.i.+pment. The user functions-like humidity, temperature and all that-can either be set and locked or left open at the s.h.i.+pper's discretion in case they need adjustment in transit."

"So you can't change the source or the destination in transit unless you have a Port Authority ident."

"Not even if you do have a PA ident. Once a setting is locked, it can't be changed until the receiver accepts the s.h.i.+pment and signs off with us. The system only lets that happen at the destination address."

"What if you hacked it, opened the box and modified the software?"

"All you'd do is cause a self-encryption verification failure. The system would halt the container at the next control point and drop a trouble flag."

"What if I supplied my own panel that allowed in-transit re-routing?"

"It still wouldn't work. Firstly, it would fail PA verification at the point of s.h.i.+pping. Second, the trans.h.i.+p net and the panel would disagree on the destination as soon as you modified it. The net would halt the container and you'd get another flag. It's fail-safe."

Fail-safe. It's a one-word lie. Nothing built by humans is fail-safe. Iknew someone was playing games with the trans.h.i.+p net. What Merral was really telling me was that I needed to look for hackers in the net's high-level control software or corruption at the Port Authority itself. I didn't tell her that: she might be the one I was looking for.

Instead I offered a compliment. "Sounds like you're pretty secure. I've seen banks with looser systems."

I meant it too. I didn't mention that I'd seen banks with looser systems because I'd gone in to investigate the frauds that had occurred at them.

"You've got to understand, there are better than two million containers in the system. Every day we move thirty thousand of them through Tiamat. The cargo value in just one of those can get into the tens of millions of crowns. We can't just lose track of one." There was pride in her voice. She was a hands-on technocrat and the trans.h.i.+p system was her baby.

The conversation was interrupted by the arrival of the conveyor crane. The rollers on the container rack slid us into the jaws of the waiting cradle. I felt like Captain Nemo being attacked by a giant squid. There was a clang as the locking dogs engaged and then we were on our way, swaying gently in the minuscule gravity field. The crane loaded us onto the roller rails at the end of our row of container racks. The cradle disconnected and the crane swung away. The rollers began spinning and our container moved off.

I watched out the windows like a kid on a train for the first time. There was a double jolt as we were loaded onto a sorter, then a gentle surge as we launched into free fall. I watched in fascination as we soared past the tops of the container racks. We spun slowly and I got a revolving view of the entire, bustling hub. To my surprise we didn't come within a hundred meters of another container. What looked like near misses from below were a trick of perspective. There was all sorts of room.

We reached the top of our parabola and began to descend. There was another surge as tunnel nineteen's container receiver pulled us in. We landed perfectly flat and I realized what the spin had been for-Maintain This End Up at All Times. The whole experience was exciting but vertigo inducing. I got my stomach back under control and looked over at Hunter. He had eschewed the human-sized observation chairs, choosing instead to curl up on top of a large tool bin that afforded him a convenient view and loosely belting himself in with some cargo straps. He looked completely at home, curse him.

I was clearly going to have to get more zero-gravity time if I was going to fit in on Tiamat.

The conveyors hummed and with a gentle swaying we slid into the yawning entrance of tunnel nineteen.

The swaying stopped as our container was grabbed by the roller tracks on all four sides of the tunnel.

Darkness fell as we left the entrance behind. Merral hit a switch on her control panel and the floodlights came on, lighting the way ahead.

Vertigo jerked at my stomach as my inner ears fought to reconcile themselves with my eyes. The containers move down the tunnels at about fifty kilometers an hour. That's not very much in the scheme of things but with the tunnel walls rus.h.i.+ng past just inches away it seems very fast indeed. The tiny pull of Tiamat's rotation is overwhelmed by the acceleration and deceleration forces along the container's axis as it's braked or speeded up to allow for other traffic in the tunnel.

My brain carefully weighed all this information and decided that I was falling headfirst down a bottomless elevator shaft. It was worse than the freefall in the hub. My knuckles were white on the arms of the chair and I found I couldn't make myself let go.

"How long will it take to get there?" I asked, trying to keep my voice calm. It came out sounding tense anyway.

"About forty minutes." It was clearly just routine to Merral.

Hunter yawned, curled up and went to sleep.

A track shunt appeared ahead of us. Luminous letters flashed by, too fast to actually read but I registered them as Y2. A black opening flashed by.

I closed my eyes and took three deep breaths and found I could relax my grip. I was just sitting in a chair in very low gravity. The seatbelt pulled gently as the container responded to the tracks and I could hear the whine of the rollers. I sat on my hands and opened my eyes.

Vertigo hit again, but I forced myself to keep sitting on my hands. Eventually I got used to the view.

Another opening, another junction and W1 flashed by. Merral had brought up a tiny hologram on her board. I recognized it as a map of the s.h.i.+pping tunnels. Tiny white dots moved slowly along its tributaries.

She pointed to one highlighted in red. "That's us."

I asked her some more questions about the trans.h.i.+p net and its security arrangements. She was happy to oblige me. I got detailed information on how data was stored, how transmissions were crypted and errors caught, how containers were sealed and how physical access was controlled. It really was an impressive system but she kept using the word "fail-safe." An engineer really ought to know better.

After a while the conversation lagged and I fell to watching the hypnotically repeating panorama of tracks, rollers and supports. P3 streaked past. I thought about Holly and Suze. P2, P1, O1, N4, N3. I stopped counting them and thought about Suze.

My reverie ended when the deceleration kicked in and pushed me against my safety belt. A scrabble of claws from behind told me that Hunter's nap had been interrupted and he'd nearly slid out of his improvised restraints. We slowed to a fraction of our former speed. A tunnel junction was coming up.

I looked in amazement at the luminous figures on the tunnel wall. J2-the container bay that didn't exist.

The floodlights illuminated a track shunt ahead, leading into a side tunnel identical to all the others we'd pa.s.sed so far. I'd expected a complex trail of trapdoor computer programs and corrupt customs checkers. I'd imagined secret doors, illicit tunnels or a Slaver device that could move cargo containers into hypers.p.a.ce pockets. I didn't know what I was looking for, but I certainly hadn't expected a perfectly normal tunnel junction, labelled with glowing letters four meters tall.

The rollers braked our container some more and we were switched onto the side track. We rocked slightly from side to side as we entered the container bay and lost the stability of being guided on all four sides. Automatic handling gear clanged as it coupled to the container's lifting lugs and slid us up a container rack. It was only four tiers high but otherwise identical to the one we'd started in at the up-axis hub. The locking dogs engaged with a solid thump and we were stopped.

Merral looked around from the side window. "Here we are," she said, as if there were nothing unusual about it. I looked out the window and I knew we'd hit paydirt. Jury-rigged spotlights lit the scene. Most of the immense bay was empty, with only a single row of empty racks, although the conveyer was built to service a dozen more. Another container was shunted onto the bay's only loading ramp. Its end doors were open and stacked around it were hundreds of white plastic crates stamped with UN code numbers.

I had gambled on finding a lead. I'd found smuggler central.

Hunter and I piled out and jumped the thirty meters to the ground. He landed in a combat-ready crouch.

I came down less gracefully but my nerves were just as taut. I drew my stunner from its holster on the belt of my patrol pack. I don't usually carry the pack but I was glad I'd brought it this time. Now I wished that I'd worn my body armor too. For the first time I noticed Hunter's only weapon was his ceremonial dagger and I realized that it was all he ever carried.

Merral came down after us, cautiously. J2 was just the disused container bay she'd expected, but she was more than smart enough to make the connections. Without words she took up a position behind us, watching the tracks leading to the container tunnel and letting us concentrate on the bay itself.

Nothing moved. I was about to relax and tell Merral there was no danger when Hunter's sharp "Siisss!"

warned me to silence. He was in a frozen crouch, his ears swivelled up and forward, twitching slightly back and forth. One paw was gesturing for quiet.

Suddenly he leapt, sailing across the vast chamber in seconds. His target was the entry to an access corridor in the opposite wall. He flew through the opening with unerring precision, landed on a handhold and took off again, down the corridor and out of sight. I followed him awkwardly. I knew I could never have the big cat's reflexes, but I fervently wished I had at least Jocelyn Merral's easy grace in microgravity. I missed my jump by better than twenty meters and floundered down while she waited patiently. The access corridor was half a klick long. I swallowed my ego and let Merral hold on to me.

She pushed off into a long parabola. A couple of kicks en route brought us to the end of the corridor.

The pressure door to the next section was closed and Hunter was examining it intently. He turned to us as we arrived.

"I heard a sound, which I now presume was this door being opened and then shut. There is fresh scent in this tunnel of a human male. He must have fled when our container's lights entered the trackway." The kzin showed his fangs and licked his chops with a deep-throatedmrrrowl . "There is much fear in his sweat."

I went to thumb the door open but the plate had been ripped open and bypa.s.sed. Not even an ARM ident would work now. Closer inspection revealed the locking mechanism. A hole had been cut in the door's plasteel surface and a simple lever and pivot engaged the securing bolts inside. A metal pin attached to a chain could be inserted to hold the lever in the locked position. With the pin in place the door was proof against anything short of heavy energy weapons. The holes rendered the door useless in a depressurization emergency, but the smugglers wouldn't be worried about that.

I tried the handle reflexively. It didn't budge.

"I have already attempted that," said Hunter mildly.

"It's clear we're not going to get through. Let's seal this bay off and get the crime scene team down here."

I grabbed the comm unit from my patrol pack and called Dispatch. I didn't get anything but static. No repeaters in this unfinished section. Our runner had made a clean getaway.

Merral noticed the problem. "There's a Port Authority comm on the control board in the container."

Hunter snarled in acknowledgement and launched himself back down the corridor, eager to be on with the chase.

I let him go, turning to Merral. "You know about this place?"

"Of course." She gestured at the door and the pirated wiring the smugglers had used to power their floodlights. "Although evidently I didn't know everything I thought I did."

"Tell me about it." We turned back down the corridor.

"This bay was supposed to serve a whole new industrial subsector they were going to put in right after the liberation. Turns out they overestimated the requirements and they never needed the s.p.a.ce, so they just sealed it off and left it."

Her explanation made sense but there were other problems. "The trans.h.i.+p net doesn't even know it exists."

We turned the accessway corner into the main bay. Hunter jumped down from the container. "The crime scene team and a detachment of Goldskins are on their way. They will open the pressure door from the other side. I will meet them there." He leapt off again without waiting for an answer.

"Of course it does," Merral continued.

"It doesn't." I paused, decided to trust her. The smugglers already knew we were on to them anyway.

"Miranda Holtzman's internal organs were found in a s.h.i.+pping container on Wunderland, along with a cache of stolen UN weapons. The container's point of origin was 19J2, but when I tried to punch up the data on it the system drew a blank."

"You did a s.h.i.+pping trace to get that data, right?"

"Yah."

She nodded. "When you do a trace, the net uses the billing system data because normally you're interested in who owns the s.h.i.+pment and who's paying for it. This bay isn't in the billing system because no customers are registered to it so it would never show up. But the routing software knows about every node around Alpha Centauri and that's the data set that gets used when a s.h.i.+pment is set up and verified."

The picture became clearer. "Is there any way someone could swap the source and destination addresses without a Port Authority ident, or at least without logging it in the computer?"